Gas chromatographic apparatus utilizing capillary columns is an extremely successful analytical device in the chemical laboratory. Such a device provides very sharp separation between similar compounds, large theoretical plate count and relatively rapid analysis speed. It utilizes a capillary column which has an inside diameter typically less than 0.5 millimeter in diameter. Columns of this sort are extremely valuable in providing very critical separations of similar compounds, but there are great difficulties in preparing the materials for delivery to the column. One difficulty is acquiring a sample sufficiently small to achieve optimal separation of constitutent components. In many instances, even where the material to be analyzed is quite small in quantity, the material must be handled in a rather gross fashion in comparison with the size of the necessary sample required for the column. It is common practice to inject an oversized sample into an inlet splitter apparatus. Some sample is always wasted which, in and of itself, is not highly desirable, but, more importantly, it is difficult to know what portion of the excessive or oversized sample has been split into the column and what portion has been wasted. Most importantly, the ratio of splitting varies somewhat with changing molecular weights of sample constituents. Some measure of proportionality must be known in advance so that sample size delivery to the column is properly controlled.
In a typical situation, the size of the sample is only a minute portion of a liter, even as small as 10.0 nanoliters. Nanoliter specimens are so small as to be usually impossible to obtain from a sample delivery system other than through the use of sample splitters and the like.
An early sample splitter utilized a type of passage with a large outlet and a small outlet. The large outlet carries away the bulk of the sample, and, hopefully, the remaining portion passing through the small outlet is precisely controlled so that the capillary column apparatus receives a known percentage of the gross sample delivered to the splitter. There have been other systems for splitless injection which are well documented in the literature. References can be consulted for various known techniques for attempting to obtain a portion of a sample free of bias arising from molecular weight.
There has been some difficulty in achieving analysis of liquids with low boiling point constitutents. The difficulty is not in the testing, per se, but, rather, in the delivery of a specimen of precise volume measure. As an example, if a specimen is maintained in a liquid state under pressure within a syringe prior to injection, a problem later arises in that injection through an elastomeric septum at high temperatures results in fractionation of the sample. Error as a result of fractional vaporization is increased when the light sample constituents partially vaporize and heavier constituents partially remain in liquid or solid form in the syringe needle after injection. This error is randomized by variations in the time the syringe remains in the inlet port.
The present invention is an apparatus which overcomes this by providing a method and an apparatus whereby the injected sample is intentionally vaporized off-line into an open loop before introduction to the separation column. Sample introduction to the gas chromatographic column is then effected either directly or after dilution and an additional sampling stage.
The present invention is uniquely able to handle these problems. Additionally, it simplifies other existing methods by reducing the complexity of preconcentration and solvent stripping techniques, while permitting introduction of smaller, but more quantitative samples.